The present invention relates to an inverter device for converting a direct current into an alternating current.
Heretofore, an inverter device shown in FIG. 1 has been known. In FIG. 1, the reference numeral (1) designates a DC power source; (2U+), (2V+), (2W+), (2U-), (2V-) and (2W-1) respectively designate transistor; (3U+), (3V+), (3W+), (3U-), (3V-) and (3W-) respectively designate diodes. The transistor and diode (2U+), (3U+); (2V+), (3V+); (2W+), (3W+); (2U-), (3U-); (2V-), (3V-) and (2W-), (3W-) are respectively connected in reversely parallel. The transistors (2U+), (2U-); (2V+), (2V-) and (2W+), (2W-) are respectively connected in series. The collectors of the transistors (2U+), (2V+), (2W+) are connected to a positive terminal of a power source (1) and the emitters of the transistors (2U-), (2V-), (2W-) are connected to a negative terminal of the power source (1). The reference (4) designates a load three terminals (U), (V), (W) of which are respectively connected to a joint of the transistor (2U+) and the transistor (2U-); a joint of the transistor (2V+) and the transistor (2V-); and a joint of the transistor (2W+) and the transistor (2W-). The bases of the transistors (2U+), (2V+), (2W+), (2U-), (2V-), (2W-) are respectively connected to the base controller (5). During the period shown in FIG. 2, the base signal is controlled so as to provide phase shifts for each 120.degree. in the transistors (2U+), (2V+), (2W+); and for each 180.degree. between the transistors (2U+), (2U-); (2V+), (2V-); and (2W+), (2W-) and to turn on for 180.degree., respectively.
When the base signal is input into the base of the transistor, the voltage shown in FIG. 3 is applied between the terminals of the load (4). The voltage of the power source (1) is shown as Ed. During the period of (I) of FIG. 2, the transistors (2U+), (2W+), (2V-) are turned on whereby a voltage Ed is applied between (U)-(V); a voltage -Ed is applied between (V)-(W) and a voltage 0 is applied between (W)-(U). This corresponds to (I) in FIG. 3. Thus, the AC is fed from the DC power source (1) to the load (4).
The diodes (3U+), (3V+), (3W+), (3U-), (3V-), (3W-) are required for forming passage capable of passing the current in the direction of the currents of the transistors which have been turned off, even though the transistors (2U+), (2V+), (2W+), (2U-), (2V-), (2W-) are turned off in the case of the induction load (4). That is, for example, when the transistor (2U+) is turned off, the diode (3U-) passes the current which has been passed through the transistor (2U+). The diode (3U-) is turned on and the potential of the terminal (U) is the same as that of the turn-on of the transistor (2U-). The voltage waveform shown in FIG. 3 is not changed.
In the inverter shown in FIG. 1, the transistors are used for the switching elements. The transistors are expensive in comparison with a thyristor etc. as another element having the same current capacity. Thus, the thyristor does not turn-off even though the gate signal is stopped. Therefore, the inverter device shown in FIG. 1 does not operate in the normal state only when the transistor is replaced to the thyristor. When the transistor is replaced to the thyristor, as it is well known, a commutation circuit is required.